1. Field of the Invention
This invention relates to physical systems identifiable via configuration parameters and, more particularly, to methodologies and concomitant systems for determining the composition of the physical system via measurements at system boundaries, including determining the composition of subscriber loops.
2. Description of the Background Art
There has been considerable recent interest in the development of techniques to determine the composition of physical structures from measurements of the physical structure at boundary points of the structure. Representative of the technology applied to the imaging of objects, such as tumors or masses, in the human body, is the technique reported in U.S. Pat. No. 5,747,810 issued to Schotland and entitled “Simultaneous Absorption and Diffusion Tomography System and Method Using Direct Reconstruction of Scattered Radiation.” As disclosed, the method for the direct reconstruction of an object from measurements of the transmitted intensity of diffusively scattered radiation is effected by irradiating the object with a source of continuous wave radiation. The transmitted intensity is related to the absorption and the diffusion coefficients of the object, which effectively determine or define the object, by an integral operator. The image of the object is directly reconstructed by executing a prescribed mathematical algorithm, as determined with reference to the integral operator, on the transmitted intensity of the diffusively scattered radiation.
With respect another class of physical structures, namely telephone subscriber loops, wherein a loop typically connects a customer with a local telephone central office and is composed of lengths of cable such as, for example 26 gauge or 24 gauge cable, there has been considerable interest shown in devising a technique to determine the composition of a loop from so-called single-ended measurements in order to qualify such loops for high-speed digital transmission. It is especially desirable to estimate the configuration of a subscriber loop from measurements made at the input of the loop at the central office. For example, one might measure the complex input impedance of the loop in the frequency domain or the time-domain echo at the input to the loop. From these measurements, the composition of the loop is estimated using identifiable characteristics in the response, such as peaks of return signals or time intervals between peaks in the response signal (generally referred to as “time domain reflectometer” approaches). Moreover, based upon estimates of the loop configuration from these measurements, it is further possible to estimate the transmission characteristics of the loop to the customer end.